32 



ELEMENTS OP BOTANY. 



nnmeroxis, and ench separfitc and distinct, or all may bo who'ly or partly 

 united. 



When the petals arc distinct the corolla is termed polypetalous 

 (Fifif. 55); when they ai'o united it is termed mono" or gamopetalous 

 (Fig. 5(!). In the gamopetalous corolla there is the same distinction of 

 tube, throat, limb, and lobes as in the gamoscpalous calyx, and it is de- 

 veloped ill the same manner — by the fusion of originally distinct leaflets. 

 It may likewise be regular (Figs. 55 and 5()) or irregular (Figs. 57 and 58), 

 and though commonly deciduous, it is sometimes withering-persistent 

 — that is, withering but not falling away f'-om the maturing fniit. In 

 short, the corolla is very like the calyx, save that it is much more delicate 

 in structure, more beautiful in foi'm, and often most exquisitely colored. 



Pio. B5. — Polypetalous corollii of a wild rose. 



Fio. 50.— Mnnopotnlous 

 corolln and mouo.sopalous 

 calyx of tobacco. 



Fio. 57. — Irrogiilnr co- 

 rolla of aconite. 



It is not unfrequently absent ; then the flower is called apetalous. In 

 this case the calyx is often colored like a corolla, and therefore well sup- 

 plies its place. But in many plants both calyx and corolla are wanting ; 

 then the dowers are termed naked. 



Tlie essential floral organs, as remarked above, are the stamens and pis- 

 tils. The stamens are variable in number, and commonly form a circle 

 within the corolla if this be present, or in its absence within the calyx. 

 Iiiey are the fertilizing organs, or, according to the former ideas of the 

 sexuality of plants, they supply the male element in the process of repro- 

 duction. 



A stamen consists of two parts, an anther and a stalk or filament 

 iipon which this is supported (Fig. 59). The anther is the only essential 

 part, and this may be and often is sessile. It consists of two cells, di- 

 vided from each other vertically by a septum, each opening at maturity and 

 yielding a cellular, powdery substance — the pollen, which is the fertilizing 



